Dynamics of hearing status in closed head injury.

Hearing impairment can be one of the more subtle deficits seen after closed head injury (CHI), and it may not be diagnosed until late in the recovery phase if at all. Most studies have assessed patients immediately after CHI. Repeated assessments at regular intervals were not performed in the majority of studies done to assess whether any initial hearing loss regressed or progressed. Follow-up at later stages will shed more light on the audiological consequences of CHI. The aim of this study was to analyze the long-term audiological consequences of CHI. A total of 290 subjects with CHI were chosen and followed-up at 3, 6, and 12 months. The audiological test battery comprised pure tone audiometry (PTA), speech audiometry, tympanometry, auditory brainstem response (ABR), and middle latency response (MLR), and was administered to all subjects. The data from 96 subjects who completed all three follow-ups were analyzed for tympanometry, ABR, and MLR. However, for PTA and speech audiometry, data from only 76 subjects were analyzed, as unconscious and disoriented subjects could not undergo these tests at initial testing. The results revealed that hearing status after CHI varies, and that at follow-up significant changes in hearing were seen. Hearing of low frequencies improved, due primarily to improvements in middle ear function. Significant changes in ABR latencies and MLR amplitudes were also observed. This reflects the unequal rates of recovery observed in the different parts of the central auditory nervous system.